Exam 14: The Mechanism of Translation

The crystal structure of the ribosome provided key new evidence that

Which component of the nucleolus is thought to be the location of active ribosomal genes?

Eukaryotic ribosomes misincorporate one amino acid for every 1,000-10,000, whereas the eukaryotic replication machinery misincorporates one nucleotide for every ~1x10⁷, a number which goes down to ~1x10⁹ following activity of the mismatch repair machinery. (a) Why can the cell tolerate a higher rate of error in translation than in replication? (b) Besides errors that occur in the ribosome, what is another potential source of error in protein synthesis?

What is the function of and where is the "peptidyl transferase" region of the ribosome? Of what is this region primarily composed?

Aminoacyl-tRNAs display high fidelity, even for amino acids such as threonine and serine that have very similar side chains. Present a model for the proofreading activity of aminoacyl- tRNA synthetases based on recent X-ray crystallographic evidence.

The start codon for translation in eukaryotes is

What would be the effect on the function of eIF2 of inhibiting its guanine exchange factor? Would the outcome be different if eIF2 were phosphorylated?

In order to recycle into its active form to bind another initiator Met-tRNA, eIF2-GDP must be converted to eIF2-GTP. Describe how this occurs and explain how this process differs from GTP hydrolysis.

Diagram the mechanism of translational control by phosphorylation of eukaryotic initiation factor 2 (eIF2), starting with activation of protein kinase RNA (PKR).

In eukaryotes, the mRNA to be translated is most likely folded into secondary and tertiary structures and coated with protective RNA-binding proteins. Discuss the importance of the 5′ cap and poly(A) tail for loading of the mRNA onto the 43S complex.

In eukaryotes, ribosomal RNAs are transcribed by

Draw a rough sketch of a ribosome, showing the location of the large and small subunits and the E, P, and A sites.

Which statement is not true about the nucleolus?

Transfer RNAs couple to amino acids by